The invention relates to articles that require surface protuberances, such as metal components used in turbine engines. In some embodiments, the invention is more specifically directed to improved techniques for increasing the heat transfer characteristics on various surfaces of the articles.
Various techniques have been devised to maintain the temperature of turbine engine components below critical levels. As an example, coolant air from the engine compressor is often directed through the component, along one or more component surfaces. Such flow is understood in the art as xe2x80x9cbackside air flow,xe2x80x9d where coolant air is directed at a surface of an engine component that is not directly exposed to high temperature gases from combustion. In combination with backside air flow, xe2x80x9cturbulatorsxe2x80x9d have been used to enhance heat transfer. Turbulators are protuberances or xe2x80x9cbumpsxe2x80x9d on selected sections of the surface of the component, which function to increase the heat transfer with the use of a coolant medium that is passed along the surface.
Turbulators are generally formed by casting. However, casting cannot readily be used to apply turbulation to certain areas of a component. For example, it is very difficult to cast protuberances on some portions of the turbine engine parts, such as on certain sections of internal cavities; in locations where there is restricted molten metal flow; or in areas where mold sections are separated during fabrication. It may also be difficult to provide turbulation to some of the external surfaces of turbine parts, such as the outer platforms of an engine nozzle.
In some instances, the turbulation on the surfaces of engine components has to be repaired or modified while the engine is in service. In other instances, it may be necessary to add turbulation to engine components during service or repair, to improve the heat transfer and cooling effectiveness at specific locations within the component. The addition and repair of turbulation cannot be achieved by the casting process.
One known technique of applying turbulation to an already formed component, is to wire-spray turbulation onto a surface of the substrate. A deficiency associated with such type of turbulation is oxidation of the coating, which reduces heat transfer effectiveness. In cased of severe oxidation, coating spallation may result with subsequent complete loss of heat transfer benefits.
Further methods for applying turbulation to various types of metal substrates would be welcome in the art. There is a need for methods that are capable of providing turbulation on surfaces that lie within cavities, and on any other surface that is not easily accessible. There is a need for methods that are capable of applying protuberances of different sizes and shapes, and in patterns. In addition, there is a need for articles having turbulation provided thereon having desirable heat transfer characteristics and durability.
One embodiment of the present invention calls for a method of providing turbulation on a surface of a substrate, including the steps of applying a layer on a surface of the substrate, the layer comprising braze alloy and turbulation material; and fusing the layer on the surface of the substrate, whereby the braze alloy bonds the turbulation material to the superalloy substrate. The layer of material may be applied to the substrate in various forms, including a brazing sheet and a slurry. In addition, the substrate may be a metal substrate, such as a superalloy substrate. Another embodiment of the invention calls for an article including a substrate and turbulation material bonded to a surface of the superalloy substrate by braze alloy. Still another embodiment calls for an article including a substrate to which is bonded turbulation material having a particular particle size. Other embodiments include a brazing sheet and a slurry including turbulation material.